In the previous article you learned how to arrange diatonic chords into a “drama.” Those chords were all triads — built from root, 3rd, and 5th. Here you’ll see how adding one more note makes the same progressions feel much more expressive.
🎨 Triads are the sketch; 7th chords are the color
In the chords article we said chords are like colors: major is bright, minor is dark. That’s the world of triads.
But “bright” comes in flavors — clean bright, jazzy bright, and bold bright are different. Triads alone can’t capture that. 7th chords change that: take a triad (root, 3rd, 5th) and add one more note, the 7th. That single note makes the chord’s character much more specific.
If triads are the “sketch,” 7th chords are the “color” — same shape (bright/dark), but with more texture and depth.
🎹 Three kinds of 7th chords
How you add the 7th gives three main types, each with a different feel. The intervals article showed how “distance” works; that’s what drives the difference here.
① Major seventh (maj7) — smooth and open
Triad plus a major 7th (the 7th scale degree — one half step below the octave).
* Cmaj7 = C + E + G + B
* Feel: open, slightly sophisticated. Think city pop, bossa nova.
* In diatonic: the 1st and 4th chords become maj7 (Cmaj7, Fmaj7).
If it sounds like “café background music,” maj7 is usually involved.
② Minor seventh (m7) — soft and bittersweet
Minor triad plus a minor 7th (one whole step below the octave).
* Dm7 = D + F + A + C
* Feel: minor’s sadness with softness. Less sharp, more floating.
* In diatonic: the 2nd, 3rd, and 6th chords become m7 (Dm7, Em7, Am7).
Dm is “sad”; Dm7 is “sad but somehow comfortable.” That small shift shapes the whole vibe.
③ Dominant seventh (7) — “I want to go home”
Major triad plus a minor 7th. A bit odd: major brightness plus tension.
* G7 = G + B + D + F
* Feel: strong tension. “I want to resolve!” much more than plain G.
* In diatonic: only the 5th chord is this type (G7).
Remember the progressions article “striker.” G7 is the striker taking the run-up — maximum “want to go home to C.”
🏟️ The diatonic team, 7th version
In the diatonic article you met the triad team. Add 7ths and everyone’s character gets clearer:
| Position | Triad | 7th chord | Type | Character change |
|---|---|---|---|---|
| 1st | C | Cmaj7 | maj7 | Stable → smooth stable |
| 2nd | Dm | Dm7 | m7 | Reflective → soft reflective |
| 3rd | Em | Em7 | m7 | Link → soft link |
| 4th | F | Fmaj7 | maj7 | Floating → dreamy floating |
| 5th | G | G7 | 7 | Tension → “go home” max |
| 6th | Am | Am7 | m7 | Bittersweet stable → soft bittersweet |
| 7th | Bdim | Bm7♭5 | m7♭5 | Unstable → subtle unstable |
The “roles” don’t change. The drama you learned in the progressions article — captain, midfielder, striker, vice-captain, link — stays the same. Only the personalities get richer.
So you can take any progression from C-8 and just 7th-ify the chords to lift the whole thing.
| Progression from C-8 | 7th version |
|---|---|
| C → G → Am → F | Cmaj7 → G7 → Am7 → Fmaj7 |
| Dm → G → C | Dm7 → G7 → Cmaj7 |
| F → G → Em → Am | Fmaj7 → G7 → Em7 → Am7 |
Play these side by side. Same drama, same structure, different atmosphere.
✋ sus chords — “erase the color once”
7th chords add a note to enrich the color; sus chords do the opposite. Replace the 3rd with another note so the chord is neither major nor minor — a suspended feel.
* Csus4 = C + F + G (3rd E replaced by 4th F)
* Csus2 = C + D + G (3rd E replaced by 2nd D)
In the chords article we said the 3rd decides major vs minor. Sus removes that 3rd, so you get an open, neutral sound.
Typical use: briefly turn a chord into sus, then resolve.Csus4 → C (suspended → stable. Relief.)
Gsus4 → G (suspended → tension. Tease then climax.)
“sus” = “suspended.” The 3rd is held in the air. The moment it resolves is where you get the punch.
✨ add9 chords — “one extra sprinkle”
add9 keeps the triad and adds the 9th (the 2nd, one octave up). No 7th in between — just one extra sparkle on top.
* Cadd9 = C + E + G + D (triad + 9th)
Same C brightness, with D adding a bit of sparkle. Works great in open-string arpeggios. Gadd9 and Cadd9 are classic “emotional” acoustic guitar sounds.
If 7th is “changing the sauce,” add9 is “a pinch of herb at the end.” The main flavor (triad) stays; you just add a hint.
🎛️ Try the “color” in OtoTheory
OtoTheory lets you use these extended chords without theory — pick by ear.
* Sound palette (chord dial)：When adding a chord, a dial-style selector lets you choose root, category, quality, and slash. Categories include “Basic” (major, minor, 7ths), “Decor” (sus4, sus2, add9). Pro unlocks “Float” (maj9, 6/9), “City” (m9, m11), “Spice” (aug, dim7). Spin the dial, hit play, add to your progression — choose and check by ear. Chord coloring becomes a game.
* Insight engine：As you build a progression, suggestions like “IVmaj7 for a dreamy feel” or “V7 for strong dominant” show context-aware extended chords. Tap to hear; compare with triads on the spot.
* Fretboard view：7th and sus chord tones show on the fretboard. You see how “one extra finger” gives 7th, or “one finger shift” gives sus4 — great for guitar and bass.
✅ Summary
One extra note on a triad changes the whole feel of a progression. Expanding chord “types” expands your expression.
* 7th chords: Add the 7th. Three types — maj7 (smooth), m7 (soft), 7 (resolve max).
* 7th-ifying the diatonic team enriches everyone; the drama stays the same.
* sus chords: Remove the 3rd for a suspended feel. Resolution gives punch.
* add9 chords: Keep the triad, add a sprinkle on top.
* Best first step: take a C-8 progression and 7th-ify it, then compare.
Next, we’ll bring in “guest” chords from outside the diatonic team — chord substitution.